Stereoisomeric forms of 4-anilido-3-methyl-piperidine-1-carboxylates

ABSTRACT

Certain stereoisomers of N-(3-methyl-1-phenethyl-4piperidyl)propionanilide having very potent analgesic activity, methods of preparing same and novel precursors therefor.

United States Patent Janssen et al.

[ 1 Sept. 23, 1975 STEREOISOMERIC FORMS OF 4-ANILlD0-3-METHYL-PIPERlDlNE-l- CARBOXYLATES Inventors: Paul Adriaan Jan Janssen,

Vosselaar; Willem Florent Maria Van Bever; Raymond Antoine Stokbroekx, both of Beerse, all of Belgium [73] Assignee: Janssen Pharmaceutica N.V.,'

Beerse, Belgium Filed: Sept. 30, 1974 Appl. No.: 510,269

Related US. Application Data Division of Ser. No. 396,277, Sept. 11, abandoned.

[52] US. Cl. 260/293.77; 424/267; 260/293.79;

rm. cm c071) 211/58 Field of Search .i 260/293.77, 293.8

Primary Examiner-Sherman D. Winters Attorney, Agent, or Firm-Salvatore R. Conte [57] ABSTRACT Certain stereoisomers of N-(3-methyl-l-phenethyl-4- piperidyl)propionanilide having very potent analgesic activity, methods of preparing same and novel precursors therefor.

10 Claims, No Drawings STEREOISOMERICFORMS OF 4-ANILIDO-3 -METIIYL-PIPERIDINE-l CARBOXYLATES CROSS-REFERENCE TO RELATED APPLICATION:

This is a divisional application of my co-pending application Ser. No. 396,277, filed Sept. 11, 1973, and now abandoned.

BACKGROUND'OF THE INVENTION components from the optically inactive parent mixture,

is given. This invention provides for the preparation and isolation of certain such isomeric components, novel compositions thereof and novel precursors therefor.

SUMMARY OF THE INVENTION There is provided by this invention certain geometric and optical isomers of N-(3-methyl-l-phenethyl-4- piperidyl)propionanilide, which isomers, in base or acid addition salt form, have significantly higher analgesic activity, for example, from about 2-16 times higher potency, based on the weight of base administered, than the prior art compounds disclosed in said US. Pat. No. 3, 164, 600, including the commercially available compound, N-( l-phenethyl-4- piperidyl)propionanilide, also known by its generic name "fentanyl. The isomeric forms of this invention may be used in base form or, more conveniently, in acid addition salt form, either alone or in combination with other therapeutically active agents in analgesia.

DESCRIPTION OF THE PREFERRED EMBODIMENTS 1 The compounds of this invention arecertain geometric and optical isomers of N-'(3-methyl-l-phenethyl-4- piperidyl)propionanilide (Formula 1):

H Me

whenthe two groups lieon opposite sides of the plane.

In addition to geometric isomerism, each of the cis and trans geometric forms can also occur in the form of optically active dextro and levo isomers (enantiomers) due to the lack of symmetry occassioned by the asymmetric carbons at the 3 and 4-positions of the piperidine ring. As used herein, the optical rotation symbol or is an expression of the total rotatory power of the whole molecule corresponding to the sum of the contributions of each such asymmetric carbon atom. 1

According to this invention, there is provided a method of synthesizing the geometric isomers (cis and trans) of (I) and the optically active and forms of such geometric isomers. i

The geometric cis and trans isomers of (I) can be prewherein. R and R, each represent a member selected from the group consisting of loweralkyl (1-6 carbons) and aralkyl, e.g., a phenyl-loweralkyl such as, benzyl, phenethyl and the like. Such separation can be accomplished by fractional crystallization techniques employing a suitable ether-alcohol mixture, preferably a mixture of from about 1 3 to about 3 1 parts by volume of a dialkyl ether and isopropanol. A solution of (II) is such mixture (warmed sufficiently to provide maximum solubility) is permitted to cool slowly to ambient temperatures (below 35C), whereupon a precipitate of the cis-(i) isomer of (11), free or substantially free of the contaminating trans-(1') isomer, is obtained. Further cooling of the filtrate (e.g., down to 10C or below'yields the trans-(i) isomer of (11), free or substantially free of the contaminating cis-(i)-isomers, as a second precipitate. 1

Each of the thus-obtained cis-(i) and trans-(:) isomers of (11) may be used as precursors for the preparation of the corresponding cis and trans isomers of (1). Using the former for purposes of exemplification, cis- )-4-(N-phenylamido)piperidine carboxylate (cis-ll) is converted to the corresponding cis-(i)-4-anilino3- methylpiperidine (cis-III) by acid or alkaline hydrolysis, for example, by treatment of (cis-II) with a large molar excess of concentrated (48%) HBr solution, preferably under reflux. After the reaction is complete, the excess acid is neutralized with a suitable base, such as, for example, an alkali metal or alkaline earth metal hydroxide, ammonium hydroxide and the like, and the cis-(i)-4-anilino-piperidin product (cis-III) is extracted with a suitable organic solvent, such as, for example, an aromatic hydrocarbon (e.g., benzene, toluene, xylene and the like), a halogenated loweralkane (e.g., chloroform, methylenechloride and the like), etc. and isolated by conventional techniques. Condensation of (cis-Ill) with an equivalent amount of a reactive is halo, preferably chloro or bromo, or a radical of formula 080 R wherein R represents a loweralkyl (l-6C) or p-tolyl, yields the corresponding cis-(1)4- anilino-3-methyl-lphenethylpiperidine (cis-IV). The reaction, preferably under reflux, is carried out in an inert organic solvent, such as, for example, an aromatic hydrocarbon (e.g., benzene, toluene, xylene and the like), a lower alkanone (e.g., 4-methyl-2-pentanone), and the like. The presence of a suitable base, such as, for example, sodium carbonate, is desirable to neutralize the acid (HX) produced during the course of the reaction. The addition of a small amount of potassium iodide may also be added to the reactants when X is halo. The thus-obtained (cis-IV) is then acylated with an appropriate acylating agent, e.g., propionic acid anhydride or halide under standard acylation conditions to yield the desired product (cis-l). Mechanical recovery (e.g., filtration) and standard purification techniques (e.g., recrystallization) of the product offers theessentially pure geometric cis isomer which is free or substantially free of the contaminating trans isomer. The foregoing reaction scheme, which is similarly applicable to the formation of the corresponding trans-(i) isomer, may be illustrated as follows:

Me Me its 48% NCOR| HN HBr Ph CM] t) cis-[ll (i) trans-ll i (1) acylation Ph-CH,CH, NH Ph-CH,CH,

cis-IV cis-l (i) trans-IV (i) trans-I (i) Attempts to resolve the aforementioned geometric cis-(i) and trans-(i) isomers of formula (I) into their respective dextro and levo optical isomers by conventional resolution and isolation techniques have not been successful.

It has now been found that such optical isomers may be obtained by the synthesis hereinafter described. This synthetic approach is based on an initial resolution of certain novel precursors described in the preparation of the aforementioned geometric isomers, namely, the (i)4-anilino-3-methyl-piperidines of formula (cis-Ill) and (trans-Ill).

It has been found that said geometric (cis-Ill)-(:)- isomer may be resolved by treatment with optically active forms of tartaric acid. At temperatures above approximately 45C both the dextro and levo 4anilino-3- methyl-piperidines form salts with (+)-tartaric acid which are extremely soluble in lower alkanols 1-6 carbons), preferably methanol, so that minimal amount of e HN I cis-ill alkanol need be employed. The addition of alower alkanone (l-6 carbons), preferably dimethyl ketone, to

heated solutions of said salts till turbidity occurs, re-

sults in the crystallization out of solution, as the temproduct which is free or substantially free of contaminating (+)-acid cis-(+)-base salt.

The mother liquor is concentrated, for example, by

evaporation in vacuo, and an aqueous solution of the residue is treated with alkali, for example, an alkali metal or alkaline earth metal hydroxide or ammonium hydroxide, to neutralize the acid that is present. Extraction of the cis-(+)-4-anilino-3-methyl piperidine base is accomplished'with chloroform. The chloroform extract 2 is then dried and evaporated and the resultant residue of cis-(+) base is treated with tartaric acid using a lower alkanol andlower alkanone according to the procedure previously described with (+)-tartaric acid. As

the temperature of this solution is lowered below approximately 35C, the ()-tartrate salt of cis-(+)-4- anilino-3-methylpiperidine crystallizes'out and is isolated. Said ()-acid cis-(+)-base salt is essentially optically pure and is free or substantially free of contaminating ()-acid cis-(-)-base salt.

The cis-()-4-anilino-3-methylpiperidine (+)-tartrate and the cis-(+)-4-anilino-3-methylpiperidine()- tartrate salts obtained by the above resolution procedure may be converted to the corresponding free base by conventional treatment with alkali, and the respective cis()- and cis-(+)-4-anilino-3-me thyl piperidines thus obtained may be utilized in the subsequent synthesis of the corresponding cis-()- and cis-(+)-isomers of formula (1).

Such synthesis comprises the steps, as previously described in the preparation of-the geometric isomers, of condensation with phenethyl halide and subsequent acylation with propionic acid anhydride or halide.

The foregoing reaction scheme may be illustrated as follows:

resolution (tartaric acid) cis-Ill Me Me acylation Ph CH,CH, NH PhCH,CH,- N-CEt Ph Ph cis-IV cis-l cis-IV ClS-l For simplicity the foregoing process has been de- TABLE 1 scribed for the preparation of cis-(+) and cis-()- somers of formulas (I). The process can be operated 10 Potency Duration in exactly the same way for the formation of the corre- Compound (wg/kg i v Ratio (mins.) sponding trans-(+)-and trans-(-)-isomers of formula (I), except that initial resolution of the geometric 3:2 :22 8:85 3% (trans-lIl)-(:)-isomer, rather than the (cis-Ill)-(i)- C. trans-(i) 0.01 2 40 isomer, with optically active forms of tartaric acid is re- 5 16 86 quired.

*As function of weight base Accordingly, there are obtained the trans-()-4- N-( l-Phenethyl-4-piperidyl)propionanilide.

lll

B -cis-(i)-N-(3-methyl-l-phenethyl-4- anilmo-3-methyl plperldine )-tartrate and pipcridynpmpionanilide oxalate trans-(+)-4-anllmo-3-methyl pipendine ()-tartrate 20 c. trans-(I)-N-(3-methyl-l-phenethyl-4- piperidyU propionanilide oxalate salts, which upon treatment with suitable base, yield cis N (3 methyl l phenmhy| 4 the corresponding free base forms. piperidyl)propionanilide nitrate isopropyl alcoholate The formula ll precursors may be obtained by treating an appropriate 4piperidone of formula (ll-a), wherein R is a member selected from the group consist- The preferred isomeric forms are the cis isomers, ing of loweralkyl and aralkyl, with aniline to form the l h i d i -(+)-form f N-(3- h Schiff base (ll-b) which is then subjected to reduction, 1- h rh 4 i id 1) i ilid h latter for example, with sodium borohydride, to yield the 4- b i t preferred i vi w of its very marked and anilino product (ll-C) which in turn is acylated with an surprisingly potent analgesic activity ppr p i y ng g n -g-i a lower alkanOiC acid In view of their useful analgesic activity, the subject or aralkanoic acid anhydride or halide, under acylating compounds may be formulated into various pharmaconditions familiar to those skilled in the art to yield ceutical forms of administration purposes. To prepare the desired precursor (II). The reaction scheme may be the pharmaceutical compositions of this invention, an

illustrated as follows: analgesically effective amount of the particular com- Me 7 Me Schiff base ROOC- O HN- ROOC- :N

formation (ll-a) (ll-b) Me Me redn acylation ROOC--- lrH ROOC Glil-CO-R (NaBH) Ph Ph (ll-c) (II) The organic bases of formula l) may be converted pound, in base or acid-addition salt form, as the active to corresponding pharmaceutically acceptable acid adingredient is combined in intimate admixture with a dition salts by reaction with an appropriate acid. e.g, an pharmaceutically acceptable carrier, which carrier may inorganic acid such as, for example, hydrochloric, hytake a wide variety of forms depending on the form of drobromic, hydriodic, sulfuric, nitric and like acids, or, preparation desired for administration. These pharmae.g., an organic acid such as, for example, acetic, propiceutical compositions are desirable in unitary dosage onic, glycolic, lactic, oxalic, malic, malonic, tartaric, from suitable, preferably, for administration orally, reccitric, sulfamic, ascorbic and like acids. in turn, the tally or by parenteral injection. For example, in preparacid addition salts may readily be converted to the coring the compositions in oral dosage form, any of the responding base forms by conventional treatment with usual pharmaceutical media may be employed, such as, suitable base. for example, water, glycols, oils, alcohols and the like The compounds of formula (I), in base form or more in the case of oral liquid preparations such as suspenpreferably in the form of a pharmaceutically acceptsions, syrups, elixirs and solutions; or sol d carriers such able acid addition salt, are highly potent analgesics, as as st h sug kaolin. lubricants, binders. n demonstrated, for example, in experimental animals. g i g agents and the like in the case Of P P According to the rat tail withdrawal test described in apsu s a ta t B aus f t ir ease in ad t OrSChung, 13, 502 (1963 21', 862 tration, tablets and capsules represent the most advan- (1971 the subject compounds demonstrate, as exemg p dosfige unit form, in which case solid P plified in Table 1, an increase in potency of from 2 to maceutwal earners are f y f p y F P 16 times, as compared against h prototype f h teral compositions, the carrier will usually comprise prior art, fentanyl. sterile water, at least in large part, though other ingre- 'dients, for example, to aid solubility, may be included.

lution or a mixture of saline and glucose solution. lnjectable suspensions may also be prepared in which case I appropriate liquid carriers, suspending agents and the like may be employed. Acid addition salts of (l), due

' I to their increased water solubility over the corresponding base form, are obviously more suitable in the preparation of aqueous compositions.

ltis especially advantageous to formulate the aforementioned pharmaceutical compositions in dosage unit form for ease of administration and uniformity of dosage. Dosage unit form as used in the specification and claims herein refers to physically discrete units suitable as unitary dosages, each unit containing a predetermined quantity of active ingredient calculated to produce the desired therapeutic effect in association with the required pharmaceutical carrier. Examples of such dosage unit forms are tablets (including scored or coated tablets), capsules, pills, powder packets, wafers,

' Grams A.l. 0.5 Lactose 999.5 Starch 250 Talc 250 Calcium Stearate A uniform mixture of the active and supplementary ingredients is prepared and filled into two-piece hard gel atin capsules.

Tablets: 5,000 Compressed tablets, each containing as the active ingredient 0.l milligrams of trans-(:t)-N- (3-methyl-l-phenethyl-4-piperidyl) pripio anilide, are prepared from the following formulation:

'Gl'ams A.l. 0.5 Starch 75 Dibasic Calcium phosphate hydrous 549.5 Calcium Stearate 2.5

The finely powdered ingredients are mixed well and granulated with 10% starch paste. The granulation is dried and compressed into tablets using starch as a disintegrant and calcium stearate as a lubricant.

Oral Suspension: The following formulation provides 5 liters of an oral suspension comprising 0.05 mg of cis- (i)-N-( 3-methyll -phenethyl-4- piperidyl)propionanilide as the active ingredient per teaspoonful (5mls.):

Grams A.l. 0.05 Sucrose 300.0 Dioctyl sodium sulfosuccinate 0.5 Bentonite 22.5 Methyl paraben 7.5 Propyl paraben. l.5 Antifoam A.F. Emulsion 0.l5 Propylene glycol 52.0 FD&C Yellow 5 0.l Sodium cyclamate 50.0 Sodium saccharin 5.0 Orange flavor 7.5 Filtered purified water, q.s., ad 5 liters Dissolve the parabens in the propylene glycol and add this solution to a solution of the sodium cyclamate, sodium saccharin an'd surcrose in half the water. Suspend the bentonite in hot (about 85C.)water and stir for 60 minutes. Add the bentonite suspension to the former solution. a v

Dissolve the sulfosuccinate in some water and dissolve the A.li in'the resulting soluti'om'Add the Antifoam A.F. Emulsion which hasbeen diluted to a lotion consistency with a=minimum amount of water and mix well. w

Add the latter solution of A.l. to the former mixture and mix well. Add the FD&C Yellow No. 5 dissolved in a small amount of water. Add the orange flavor, q.s. to volume with water, and stir to a-homogeneous mixture. Pass the mixture through a colloid. mill and fill suitable containers." p

. lnjectable solution: The following formulation provides 1 liter of a parenteral suspension comprising 0.031 mg of trans-(i)-N-(3-methyl-l-phenethyl-4- piperidyl)propionanilide oxalate as the active ingredient per milliliter:

Grams/l 0.031 Methyl paraben 0.250 Propyi paraben 0.025

Water for lnjection,, U.S.P.,q.s. ad Lliter Dissolve 25 gr methyl paraben and 25 gr propyl paraben in about 20 I water for injection by heating to nearly boiling (C). Add to the hot solution (about 80C) trans-(i )-N 3-methyll -phenethyl-4- piperidyl)propionanilide oxalate (the equivalent of 2.5 gr of the base).'After solutionfis complete, add water for injection to a total volume of liters. Let stand the solution to cool for at least 12 hours, then correct the volume by addition of water forinjection. After mixing, sterilize the solution by filtration (U.S.P. XVII p.81 1) and -fill in sterile containers. Sterilization may also be effected by heat. (U.S.P. Xvn p. 810 20 minutes at 121C).

Suppository: Hundred suppositories, each containing 0.05 mg of cis-(+) -N-(3-methyl-l-phenethyl-4- piperidyl)propionanilide are prepared from the following formulation:

. Grams A.l. e 0.00s Theobroma oil 50.0

Shred or grate the theobroma oil. Pulverize the Al and pour on top of the grated theobroma oil in a mortar and stir with spatula until fairly well mixed. Then grind the mixture with a pestle until a mass is formed and cut and shape into suppositories.

Capsules: 10,000 hard gelatin capsules each contain- .ing 0.01 mg of cis-(+)-N-(3-methyl-l-phenethyl-4- piperidyl)propionanilide as the active ingredient are prepared according to the following formula. These ingredients are intimately mixed together and placed into two-piece gelatin capsules.

Grams A.l. 0.1 Lactose 699.9 Talc 150 Starch 150 Calcium Stearate Grams A.l. 0.05 Starch 7S Dibasic Aqueous Calcium-phosphate 574.95 Calcium Stearate 3.5

The optically inactive compounds of formulas II and ll-C, as well as the geometric eis and trans isomers, each free or substantially free of the other, of formulas 11, Ill and 1V, and the optically active and isomers of formulas Ill and 1V, again each free or substantially free of its opposite enantiomer, are believed to be novel compounds, and, in view of their utility as precursors in the syntheses heretofore described, such compounds constitute an additional aspect of this invention.

The following examples are intended to illustrate, but not to limit, the scope of the present invention. Unless otherwise stated, all parts are by weight.

EXAMPLE 1 A mixture of 32 parts of methyl 3-methyl-4-oxo-lpiperidinecarboxylate, 22 parts of aniline, 160 parts of toluene and a few crystals of p-toluenesulfonic acid is stirred and refluxed for 2 hr. 30 min. using a waterseparator. The toluene is evaporated and the residue is distilled, yielding 38 parts of methyl 3-methy1-4- (phenylimino)- l -piperidinecarboxylate; bp. 149l58C at 0.1-0.4 mm pressure.

To a stirred mixture of 38 parts of methyl 3-methyl-4- (phenylimino)-l-piperidinecarboxylate in 130 parts of methanol are added portionwise 5.3 parts of sodium borohydride at a temperature of 30C (slightly exothermic reaction). After the addition is complete, the whole is stirredfor one hour at'a temperature of about 50C; Then there are added about 70 parts of water.

The reaction mixture is concentrated to a volume of about parts and the product is extracted with benzene. The extract is dried and evaporated. The oily residue is distilled, yielding (i)-methyl 4-anilino-3-methyll-piperidinecarboxylate as a yellow oil.

A mixture of 248.5 parts of (i)-methyl 4-anilido-3- methyl-l-piperidinecarboxylate, 198 parts of propionic anhydride and 1,200 parts of toluene is stirred and refluxed overnight to produce (i)-methyl 3-methyl-4- (N-phenylpropionamide )-piperidine- 1 -carboxylate in situ. The reaction mixture is cooled, alkalized with diluted sodium hydroxide solution, while keeping the temperature below 30C. The toluene phase is washed twice with water, dried and evaporated. The semi-solid residue of (:)-methyl 3-methyl-4-(N phenylpropionamide) piperidineJ-carboxylate (formulall) is triturated in 1200 parts diisopropylether, cooled in ice-bath and the product is filtered off, washed with diisopropylether and dried in vacuo, yielding 213.5 parts of products, which is recrystallized twice from a (1 1) mixture of diisopropyllether and 2-propanol (filtrates l and 2 are set aside), yielding about 56 parts of cis-(i)-methyl 3methyl-4-(N- phenylpropionamide)piperidine -l-carboxylate; mp. l53-154.3C.

The combined filtrates 1 and 2 are evaporated. The residue is crystallized from a l 1) mixture of diisopropylether and 2-propanol; yielding first at room temperature a fraction of about 42 parts of impure cis-(i)- methyl 3-methyl-4-(N- phenylpropionamide)piperidine-l-carboxylate, and on cooling to 0C, a second fraction of about 29 parts of impure trans-(i)-methyl 3-methyl-4-(N- phenylpropionamide)piperidinel -carboxylate. The latter fraction is recrystallized from the same solventmixture, yielding about 20.5 parts of trans-(:)-methyl 3-methyl-4-N-phenylpropionamide)piperidine-lcarboxylate; mp. l32.5134.2C.

' EXAMPLE n A mixture of parts of cis-(i)-methyl 3-methyl-4- (N-phenylpropionamide)piperidine-1-carboxylate and 750 parts of hydrobromic acid solution 48% is stirred and refluxed for 3 hours. The reaction mixture is cooled and alkalized with sodium hydroxide solution. The free base, cis-(i)-4-anilino-3-methylpiperidine, is extracted with toluene, the extract is dried, filtered and evaporated. The oily residue is distilled; yielding 74 parts of cis-(:)-4-anilino-3-methylpiperidine, bp. C at 0.4 mm pressure, which solidifies on standing at room temperature; mp. 54.6-56C.

A mixture of 11.1 parts of phenethylbromide, 11.4 parts of cis-(i)-4-anilino-3-methylpiperidine, 13 parts of sodium carbonate and 0.5 parts of potassium iodide in 400 parts of 4-methyl-2-pentanone is stirred and refluxed for 20 hours. The reaction mixture is filtered several times until clear and the filtrate is evaporated. The oily residue is dissolved in 800 parts of diisopropylether. The solution is treated with activated charcoal, filtered and the filtrate is evaporated again, yielding 16.2 parts of cis-(i)-4-anilino-3-methyl-1- phenethylpiperidine.

A mixture of 15 parts of cis-(i)-4-anilino-3-methyll-phenethylpiperidine in 320 parts of toluene is dried azeotropically. After cooling to about 40C, there are added 13 parts of propionic anhydride and the whole is stirred at reflux temperature overnight. The reaction vll mixture is cooled, alkalized with ammonium hydroxide solution and the organic layer is separated. The latter is dried, filtered and evaporated. The residue of cis- (i)-N-( 3-methyl-1 -phenethyl-4- piperidyl)propionanilide is dissolved in acetone and to this solution isadded a solution of 6.3 parts of oxalic acid dihydrate in acetone. The crystallized salt is filtered off and recrystallized from 2-propanol, yielding l2 parts of cis-(- *-)-N-(3-methyl-l-phenethyl-4- piperidyl)propionanilide oxalate; mp l63.7C

EXAMPLE III A mixture of 20 parts of trans-(:)-methyl 3-methyl- 4-( N-phenylpropionamide )piperidinel -carboxylate and 300 parts of hydrobromic acid solution-48% is stirred and refluxed for 2 hr. 30 min. The reaction mixture is poured onto crushed ice and alkalized with sodium hydroxide solution 60%. The free base, trans-(i)- 4-anilino-3-methylpiperidine, is extracted three times with toluene. The combined extracts are dried, filtered and evaporated, yielding 12 parts of trans-(i)-4- anilino-3-methylpiperidine.

A mixture of 11.4 parts of phenethylbromide, [2 parts of trans-(i)-4-anilino-3-methylpiperidine, 8.5 parts of sodium carbonate and 240 parts of 4-methyl-2- pentanone is stirred and refluxed overnight (about 15 hours). The reaction mixture is filtered and the filtrate is evaporated. The residue of trans-(i)-4-anilino-3- methyl-l-phenethylpiperidine is dissolved in acetone and the solution is acidified with an excess of 2- propanol previously saturated with gaseous hydrogen chloride. The precipitated salt is filtered off and dried, yielding 7 parts of trans-(i)-4-anilino-3-methyl-lphenethylpiperidine dihydrochloride.

From 7 parts of trans-(:)-4-anilino-3-methyl-lphenethylpiperidine dihydrochloride the free base is liberated with ammonium hydroxide solution. After extraction with toluene, the extract is dried and filtered. The filtrate is dried azeotropically and after cooling to about 40C, there are added 4.9 parts of propionic anhydride. The whole is stirred at reflux temperature overnight. The reaction mixture is cooled, alkalized with ammonium hydroxide solution and the aqueous phase is extracted with chloroform. The chloroform extract is dried, filtered a'nd evaporated. The residue of trans-(i)-N-( 3-methyll -phenethyl-4- piperidyl)propionanilide is dissolved in acetone and to this solution is added oxalic acid dihydrate dissolved in acetone. The crystallized oxalate salt is filtered off, dried and recrystallized from 2-propanol, yielding 1.5 parts of trans-(i)-N-(3-methyl-l-phenethyl-4- piperidyl)propionanilide oxalate; mp. 159.9C

EXAMPLE [V A mixture of 99 parts of cis-(- '-)-4-anilino-3- methylpiperidine and 78.15 parts of (+)-tartaric acid is dissolved in a minimal amount of methanol. To this boiling solution is added dimethyl ketone, till turbid. Filtration affords 70 parts of the (+)-tartrate salt of cis- ()-4-anilino-3-pipecoline, which can be converted to the free base by treatment with alkali (e.g., 50% NaOl-l).

' The filtrate is concentrated in vacuo and the residue is dissolved in water. The solution is alkalized with a 50% sodium hydroxide solution and extracted three times with chloroform. The extracts are dried and evaporated in vacuo. The residue is dissolved in a minimal amount of methanol together with 45.26 parts of ()-tartaric acid. To this boiling solution is added dimethyl ketone till turbid. Upon cooling, the precipitated (-)-tartrate salt of cis-(+)-4-anilino-3- methylpiperidine is filtered off and converted-into the free base with 50% NaOH. After the extraction of the free base with chloroform, the latter is dried and evaporated in vacuo to yield a residue of 33 parts of cis-(+)- 4-anilino-3-methylpiperidine; a (4% in methanol) +6.1"; m.p. 93.594.5C.

EXAMPLE v A mixture of 6.25 parts of phenethylbromide, 5.55 parts of cis-(+)-4-anilino-3-methylpiperidine, 6.5 parts of sodium carbonate, 0.] parts of potassium iodide and 200 parts of 4-methyl-2pentanone is stirred and refluxed overnight. The reaction mixture is cooled, filtered and the filtrate is evaporated in vacuo. The residue of cis-( +)-4-anilino l -phenethyl-3- methylpiperidine is converted into the hydrochloride salt in 2-propanol a mixture of the monoand dihydrochloride salt is obtained. The free base is liberated by A conventional treatment with alkali (50% NaOH) yielding 5.6 parts of cis-(+)-4-anilino-l-phenethyl-3 methylpiperidine; a(4% in methanol): +44.8

A mixture of 14.5 parts of cis-(+)-4-anilino-l-' phenethyl-3-methylpiperidine, 7.8 parts of propionic anhydride and 400 parts of toluene is stirred and refluxed overnight (about 15 hours). The reaction mixture is cooled, alkalized and extracted with aqueous ammonia. The organic phase is washed twice with water, dried and evaporated in vacuo. The residue of cis- (+)-N-( 3-methyll -phenethyl-4- piperidyl)propionanilide is converted into the nitrate salt in diisopropylether. The salt is filtered off and crystallized from a mixture of diisopropylether and 2- propanol, yielding 19 parts of cis-(+)-N-(3-methyl-lphenethyl-4-piperidyl)propionanilide nitrate isopropyl alcoholate; mp. 95.4C; ago +0.2. (2% in methanol).

A mixture of 2.9 parts of cis-(+)-4-anilino-lphenethyl-3-methylpiperidine, 2.6 parts of propionic anhydride and 200 parts of toluene is stirred and refluxed overnight. The reaction mixture is cooled and water is added. The whole is alkalized with ammonium hydroxide solution and the layers are separated. The aqueous phase is extracted twice with toluene. The combined organic layers are dried, filtered and evaporated in vacuo. The residue is converted into the oxalate salt. The salt is filtered off and crystallized twice from a mixture of diisopropylether and Z-propanol, yielding 1.8 parts of cis N-(3-methyl-l-phenethyl- 4-piperidyl)propionanilide oxalate; mp. l05.5C; a (4% in methanol) +7.04.

We claim:

l A method of preparing the cis-(i)-isomeric form of a '(1:)-4-anilido-3-methyl-piperidinecarboxylate of thefonnula: i

wherein R and R each represent a member selected from the group consisting of loweralkyl and phenyllower alkyl, which comprises cooling a solution of said (:t)-4-anilido-3-methyl-piperidinecarboxylate in a mixture of from about 1 3 to about 3 l parts by volume of a dialkyl ether and an alkanol, each having a total of six carbons, to below 35 and mechanically separating the insoluble cis-(i)-isomer, substantially free of the trans-(i)-isomer 2. A method of preparing the trans-(i-)-isomeric form of a (i) -4-anilido-3-methylpiperidinecarboxylate of the formula:

Me RooC- Gib-CO-R,

wherein R and R each represent a member selected from the group consisting of loweralyl and phenyl lower alkyl, which comprises cooling a solution of said (i)-4-anilido-3-methyl-piperidinecarboxylate in a mixture of from about 1 3 to about 3 1 parts by volume of a dialkyl ether and an alkanol, each a total of six carbons, to below 35C, mechanically separating the insoluble cis-(i)-isomer, further cooling the solution to below C and mechanically separating the insoluble trans-(i)-isomer, substantially free of the cis-(i)- isomer.

3. A method of preparing cis- (i)-methyl 3-methyl-4- (N-phenylpropionamide )piperidinel -carboxylate, which comprises cooling a solution of (i)-methyl 3- methyl-4-( N-phenylpropionamide )-pipen'dinel carboxylate in approximately equal parts by volume of a dialkyl ether and an alkanol, each having a total of six carbons, to below 35C and mechanically separating the insoluble cis-(i)-methyl 3-methyl-4-(N- phenylpropionamide)-piperidinel -carboxylate, m.p. l53-l54.3C, substantially free of the trans-(:)- isomer.

4. The method of claim 3 wherein said dialkyl ether is diisopropylether and said alkanol is 2-propanol.

5. A method of preparing trans-(i)-methyl 3-methyl- 4-( N-phenyl-propionamide )piperidinel carboxylate, which comprises cooling a solution of (id-methyl 3- methyl-4-( N-phenylpropionamide )piperidine l carboxylate in approximately equal parts by volume of a dialkyl ether and an alkanol, separating the insoluble cis-(i)-methyl 3-methyl-4-(N- phenylpropionamide)piperidine-1-carboxylate, further cooling the solution to below 10C and mechanically separating the insoluble trans-(i)-isomer, m.p. l32.5-l34.2C, substantially free of the cis-(i)- isomer.

6. The method of claim 5 wherein said dialkyl ether is diisopropylether and said alkanol is 2-propanol.

7. Cis-(i)-loweralkyl 3-methyl-4-(N- phenylpropionamide )-piperidinel -carboxylate.

Cis-(' *-)-methyl 3-methyl-4-(N- phenylpropionamide )-piperidinel -carboxylate.

9. Trans-(:Howe ralkyl 3-methyl-4-( N- phenylpropionamide )-piperidinel -carboxylate.

10. Trans-(i)-methyl 3-methyl-4-(N- phenylpropionamide )-piperidinel -carboxylate.

UNITED STATES PATENT AND TRADEMARK OFFICE CERTIFICATE OF CORRECTION PATENT N0. 3, 907, 811

DATED September 23, I975 INVENTOR(S) Paul Adriaan Jan Janssen et al.

Itis certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:

In Column 2, line 36, "(II) is" should read (II) in In Column 4, line 20, (-)tartaric" should 0 read (-)-tartaric In Column 5, line 23, "4 piperidone" should read 4-piperidone I In Column 6, line 55, "from" should read form In Column 8, line 45, "25" should read 2.5 (both instances) In Column 12, line 16, "methyl-2pentanone" should read methyl-Z-pentanone In Column 12, line 19, "anilinol-" should read anilino-l- Signed and Scaled this First Day Of November 1977 [SEAL] Attest:

RUTH C. MASON LUTRELLE F. PARKER Attesting Oflicer Acting Commissioner of Patents and Trademarks 

1. A METHOD OF PREPARING THE CIS-($)-ISOMERIC FORM OF A ($)-4-ANILIDO-3-METHYL-PIPERIDINECARBOXYLATE OF THE FORMULA:
 2. A method of preparing the trans-( + or - )-isomeric form of a ( + or - ) -4-anilido-3-methyl-piperidinecarboxylate of the formula:
 3. A method of preparing cis-( + or - )-methyl 3-methyl-4-(N-phenylpropionamide)piperidine-1-carboxylate, which comprises cooling a solution of ( + or - )-methyl 3-methyl-4-(N-phenylpropionamide)-piperidine-1-carboxylate In approximately equal parts by volume of a dialkyl ether and an alkanol, each having a total of six carbons, to below 35*C and mechanically separating the insoluble cis-( + or - )-methyl 3-methyl-4-(N-phenylpropionamide)-piperidine-1-carboxylate, m.p. 153*-154.3*C, substantially free of the trans-( + or - )-isomer.
 4. The method of claim 3 wherein said dialkyl ether is diisopropylether and said alkanol is 2-propanol.
 5. A method of preparing trans-( + or - )-methyl 3-methyl-4-(N-phenyl-propionamide)piperidine-1-carboxylate, which comprises cooling a solution of ( + or - )-methyl 3-methyl-4-(N-phenylpropionamide)piperidine-1-carboxylate in approximately equal parts by volume of a dialkyl ether and an alkanol, separating the insoluble cis-( + or - )-methyl 3-methyl-4-(N-phenylpropionamide)piperidine-1-carboxylate, further cooling the solution to below 10*C and mechanically separating the insoluble trans-( + or - )-isomer, m.p. 132.5*-134.2*C, substantially free of the cis-( + or - )-isomer.
 6. The method of claim 5 wherein said dialkyl ether is diisopropylether and said alkanol is 2-propanol.
 7. Cis-( + or - )-loweralkyl 3-methyl-4-(N-phenylpropionamide)-piperidine-1-carboxylate.
 8. Cis-( + or - )-methyl 3-methyl-4-(N-phenylpropionamide)-piperidine-1-carboxylate.
 9. Trans-( + or - )-loweralkyl 3-methyl-4-(N-phenylpropionamide)-piperidine-1-carboxylate.
 10. Trans-( + or - )-methyl 3-methyl-4-(N-phenylpropionamide)-piperidine-1-carboxylate. 